Acrylic process aid for vinyl foam extrusion

ABSTRACT

The present invention relates to an acrylic process aid useful in vinyl foam extrusion. The process aid is an acrylic copolymer containing from 50 to 79 weight percent of methyl methacrylate monomer units and has a Tg of less than 90° C., preferably less than 70° C., and more preferably less than 65° C. PVC and CPVC foams containing this acrylic process aid fuse faster at the same temperature, or fuse in the same time at lower temperatures than foam formulations currently used.

FIELD OF THE INVENTION

The present invention relates to an acrylic process aid useful in vinylfoam extrusion. The process aid is an acrylic copolymer containing from50 to 79 weight percent of methyl methacrylate monomer units and has aTg of less than 90° C., preferably less than 70° C., and more preferablyless than 65° C. PVC and CPVC foams containing this acrylic process aidfuse faster at the same temperature, or fuse in the same time at lowertemperatures than foam formulations currently used.

BACKGROUND OF THE INVENTION

Polyvinyl chloride (PVC) and chlorinated PVC (CPVC) can be foamed toprovide lighter, less expensive articles. It is important that the PVCfoams fuse quickly to allow for sufficient melt strength for foaming.PVC and CPVC foams can be developed via physical blowing agents orchemical blowing agents. Process aids are typically used to provide meltstrength. Process aids can also facilitate the fusing process. Acryliccopolymer fusion aids that have at 80 weight percent and greatermethylmethacrylate units have been used.

US 2009111915 by Applicant describes an improved acrylic copolymer foruse in highly filled PVC flooring, pipe and siding. The copolymer has alower MMA content, and a lower Tg than previously used acryliccopolymers

There is a desire to produce PVC foams at lower operating temperatures.Lower operating temperatures save energy costs, improve productappearance, and also provide a safer working environment.

Applicant has surprisingly discovered that the use of an acryliccopolymer process aid with a lower level of methyl methacrylate monomerunits than currently used can effectively used in PVC foam manufacture,providing the same level of fusion at lower temperatures, or a higherlevel of fusion at the same temperature, when compared to the acryliccopolymer process aids currently used having higher Tgs. A decreasedprocessing temperature of up to 10° C., with the same level of fusion,have been seen using the improved acrylic copolymer of the invention.Further, lower operating temperatures allow for faster downstreamcooling, offering potentially faster production speeds and improvedproduct quality/appearance due to less heat history of the polymer.

SUMMARY OF THE INVENTION

The invention relates to a foamed material comprising:

a. 50 to 99 percent polyvinyl chloride (PVC) or chlorinated polyvinylchloride (CPVC) foam matrix;

b. 1 to 15 weight percent of one or more acrylic copolymers, whereinsaid acrylic copolymer comprises from 50 to 79 weight percent of methylmethacrylate units, and from 20 to 50 weight percent comprising at leastone other acrylic monomer, wherein said copolymer has a Tg of less than90° C.;

c. 0 to 25 weight percent of filler; and

d. optionally other adjuvants;

the total adding to 100 weight percent.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to the use of an acrylic copolymer having a lowerlevel of MMA units, and thus a lower Tg, as a processing aid for PVC andCPVC foam manufacture. The acrylic copolymer process aid provides forfaster fusion at the same process temperature, or equivalent fusion at alower process temperature.

Acrylic Copolymer

The process aid of the invention is an acrylic copolymer. By “acrylic”“copolymer”, as used herein, includes copolymers, terpolymers and otherpolymers containing two or more different alkyl methacrylate and/oralkyl acrylate monomer units and mixtures thereof. The copolymers may berandom, block, tapered, comb, star or other polymer architecture. Thealkyl methacrylate monomer units are preferably methyl methacrylate(MMA), which may make up from 50 to 79 weight percent, more preferablyfrom 50 to 75 weight percent, and even more preferably 50 to 70 weightpercent of the monomer mixture. The remaining weight percent of thepolymer, is composed of at least one other alkyl acrylate and/or alkylmethacrylate type of monomer units, and may also include otherethylenically unsaturated monomers. Other (non-acrylic) monomers usefulin the copolymer composition include, but are not limited to, styrene,alpha methyl styrene, acrylonitrile, and crosslinkers may also bepresent in the monomer mixture. The Tg of the acrylic copolymer is lessthan 90° C., preferably less than 80° C., more preferably less than 70°C., even more preferably less than 65° C., and even less than 60° C. Inaddition to the methyl methacrylate monomer units, other methacrylateand acrylate monomers useful in the monomer mixture include, but are notlimited to, methyl acrylate, ethyl acrylate and ethyl methacrylate,butyl acrylate and butyl methacrylate, iso-octyl methacrylate andacrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate andstearyl methacrylate, isobornyl acrylate and methacrylate, methoxy ethylacrylate and methacrylate, 2-ethoxy ethyl acrylate and methacrylate,dimethylamino ethyl acrylate and methacrylate monomers. Alkyl (meth)acrylic acids such as methyl acrylic acid and acrylic acid can be usefulfor the monomer mixture. A preferred acrylic copolymer is one formedfrom methyl methacrylate (MMA) and butyl acrylate (BA) monomer units. Inthe MMA/BA copolymer, the level of MMA is 79 weight percent or less,preferably 75 weight percent or less, and even more preferably 70 weightpercent or less, and the level of BA monomer units is 21 weight percentor greater, preferably at least 25 weight percent or greater, and evenmore preferably 30 weight percent or greater.

The acrylic copolymer is present in the composite at a level of from 1to 15 weight percent, preferably from 3 to 12 weight percent, and morepreferably from 4 to 9 weight percent. The acrylic copolymer should bemiscible with PVC and/or CPVC. The weight average molecular weight ofthe acrylic copolymer is in the range of from 2 million to 10 million,preferably from 3 million-8 million, and more preferably from 4.0million to 7.0 million g/mol.

The acrylic copolymer is generally formed into a powder or granules foruse in the PVC foam. The powder may be formed by typical means, such asspray drying, drum drying, freeze drying, vacuum drying, or coagulationby physical or chemical means. The acrylic copolymer may be supplied foruse in manufacture in a convenient form, including but not limited to apowder, granules or pellets.

The polyvinyl chloride (PVC) or chlorinated polyvinyl chloride (CPVC)resin is of a particle size and molecular weight typically used for themanufacture of foam articles.

Blowing Agents

Blowing agents useful in the invention can be either chemical orphysical blowing agents, or a mixture thereof. In the case of a chemicalblowing agent, the gas is created by decomposition of a chemical heatedabove its degradation temperature. In the case of the physical blowingagent, gas is introduced into the polymer either directly or throughevaporating a liquid foaming agent by heating it above its evaporationtemperature. Chemical blowing agents are mainly used for higher densityfoams—down to 70% density reduction, while physical blowing agents canproduce light foams—upwards of 10× density reduction.

The chemical blowing agent can be a solid or fluid. Useful blowingagents include, but are not limited to, azodicarbonamide,azodiisobutyronitile, sulfonylsemicarbazide, 4,4-oxybenzene, bariumazodicarboxylate, 5-Phenyltetrazole, p-toluenesulfonylsemicarbazide,diisopropyl hydrazodicarboxylate, 4,4′-oxybis(benzenesulfonylhydrazide),diphenylsulfone-3,3′-disulfohydrazide, isatoic anhydride,N,N′-dimethyl-N,N′dinitroterephthalamide, citric acid/sodiumbicarbonate, monosodium citrate/anhydrous citric acid,trihydrazinotriazine, N,N′-dinitroso-pentamethylenetetramine, andp-toluenesulfonylhydrazide. Mixtures of blowing agents are alsocontemplated by the invention.

Chemical blowing agents are typically either admixed as a powder withthe PVC or CPVC composition in a mixer, or added at the extruder aspellets.

Filler and Other Additives

The PVC or CPVC composition may optionally include filler, andpreferably contains from 1 to 25 percent of filler, and more preferablyfrom 2 to 10 weight percent—based on the weight of the PVC. Typicalfillers used in PVC and CPVC foams include, but are not limited tocellulosic fibers, calcium carbonate, rosin, limestone, aluminumtrihydrate, quartz, and silica. The mean particle size of the filler isthat typically used in a foam application. In general, the mean fillerparticle size is in the range of 0.07 to 100 microns, preferably from0.5-3 microns, more preferable from 0.6-1.5 microns.

The PVC foam composition may also contain other adjuvants such as dyes,colorants, UV stabilizers, anti-oxidants, pigments, heat stabilizers,PVC homopolymer, process aids, plasticizers, lubricants, calciumstearate, metal release agents, polyethylene, paraffin wax, impactmodifiers (especially in siding), TiO₂, and others as known in the art.

A nucleating agent is sometimes used to aid in foam formation.

The acrylic copolymer and other additives may be added directly to thePVC or CPVC composition, or may be pre-blended into a masterbatch toimprove blending and manufacturing control.

The process for foam production using a chemical blowing agent isusually performed in an extruder. By “extruder” as used herein is meanta thermoforming device in which a homogeneous mixture of the polymer,blowing agent, and other additives exits as a foam. Useful extruders ofthe invention include, but are not limited to single and double screwextruders, blow molding devices, and injection molding devices. In thecase of a single or double screw extruder producing a film, sheet,profile, tube, pipe, or rod, the process of extrusion and sizing is acontinuous process. In blow molding and injection molding the process isnon-continuous, and results in an article of a part for an article. ThePVC, acrylic copolymer, filler and other additives are heated inside theextruder above its melting point in the presence of foaming andnucleating agents. When a chemical foaming agent is used, thetemperature is raised above the decomposition temperature of the foamingagent, generating gas, which is then absorbed by the molten polymerunder high pressure. Alternately, gas or fluid can be injected into themolten polymer. Gasses are excellent plasticizers for polymers.

Ideally, the polymer/gas mixture has sufficient melt strength andviscosity when it exits the die and is exposed to the atmosphericpressure. At this point, the gas dissolved in the polymer comes out ofsolution and generates gas cells in the polymer. These cells grow untilthe gas in the polymer is depleted and the polymer is further cooleddown, resisting further expansion. The foam expansion ceases once thereis a balance between the gas pressure in the bubble and the extensionalviscosity of the polymer melt. During this process, the foam is commonlysent through a sizer.

The lower Tg acrylic copolymer of the invention allows for theprocessing of PVC and CPVC foam at lower temperatures and/or fasterfusion of PVC foam compounds at similar temperatures. For PVC and CPVCfoam, fusion must first occur to ensure adequate melt strength tocapture and contain the gas from the chemical or physical blowing agent.The timing of fusion is very important, as one must balance the fusionof the PVC or CPVC compound with the generation of gas from thedegradation of the chemical blowing agent. The net effect is a widerprocessing window for the polymer matrix, allowing a wider variety ofequipment and processing conditions to combine for good quality foamproducts. While increased processing temperatures can shorten fusiontime, they also shorten the time to gas evolution from the chemicalblowing agent. This invention offers the potential to fuse the PVC orCPVC compound faster at the same processing temperature, which will notmaterially affect the time to gas evolution from the chemical blowingAgent. The lower Tg of this process aid increases the entanglement ofthe PVC or CPVC resin, which allows for a better transfer of energy fromthe extruder to the formulation. This better transfer allows for aquicker fusion time at a given processing temperature. Additionally, thesame effect can allow for similar fusion time at a lower processingtemperature. It has been found that the acrylic copolymer of theinvention can provide as much as a 10° C. cooler processing temperaturefor similar fusion profile. Cooler operating temperatures allow forquicker downstream cooling, which offer the benefit of potential fasterproduction speeds, or improved product quality/appearance due to lessheat history of the polymer. Additionally, it saves on energy costs/unitextruded.

The PVC or CPVC foam of the invention has good mechanical stability andload bearing properties. The foamed structure has a density that is atleast 3% less than said non-foamed PVC, and more preferably at least 25%less. The density reduction could be 35% less, 50% less and even as highas 100 times less dense than the non-foamed PVC material. Anotherbenefit of maintaining similar fusion while operating at lowertemperatures is a decreased heat history of the polymeric foam melt. Inmany applications, the foam is cooled slowly and the long heat historyof the slow cooling can lead to discoloration of the foamed article. Thelower processing temperatures, however, aid in shortening the coolingtime and thus improving the foamed articles color.

Preferably, the foam cell size is as small as possible. The cell sizecould be as small as 1 micron. Generally the cell size is in the rangeof from 10 to 250 microns, more typically in the range of from 50 to 150microns.

An advantage of PVC foamed structures is their higher strength-to-weightratio. Another advantage of the foamed structure of the invention is anincreased impact resistance, increased hysteresis, reduced dielectricconstant, and increased compressibility over non-foamed PVC. The foamedstructures also provide increased insulation—both thermal and soundinsulation to articles made from the foamed structure.

The foamed PVC structures of the invention could be used in the sameapplications as their solid counterparts. They would have the advantageof being lighter, saving shipping costs and making handling easier.Since the structures are lighter, they could find application wherelight weight is important, for example insulation panels, pipingincluding foamed-core piping, trim pieces, and decking products.

EXAMPLES

A typical PVC foam formulation without blowing agent (see Addendum,Table 1), was blended using a common high-intensity mixer. Theformulation was then tested in a torque rheometer, a standard industrytool. The torque rheometer test shows that fusion time of the polymercan be shortened at the same temperature. Repeating the test at lowertemperatures shows that equivalent fusion times can be at a lowertemperature. Table 2 shows the temperatures tested, while Table 3 showsthe fusion times experienced. Further, a pair of match fusion points areshown in Table 4, displaying that processing conditions can beapproximately 10° C. cooler.

It should be noted that testing showed that the new process aid does notincrease fusion torque or equilibrium melt viscosity when tested atequivalent temperatures. However, as with most polymer systemsprocessing at a lower temperature will result in increased fusion torqueand melt viscosity.

TABLE 1 Formulation Used Add* phr** phr** PVC Resin K-57 resin start100.00 100.00 Tin-based Heat Thermolite 161 start 2.50 2.50 StabilizerLubricants Calcium Stearate 66 C. 0.70 0.70 Parrafin Wax 66 C. 1.00 1.00Oxidized Polyethylene Wax 66 C. 0.20 0.20 High Molecular CommercialProcess Aid 72 C. 7.50 — Weight Process Developmentatl Process Aid 72 C.— 7.50 Aid Low Molecular Plastistrength 770 72 C. 2.00 2.00 WeightProcess Aid Filler Treated Calcium Carbonate 88 C. 5.00 5.00 PigmentTitanium Dioxide 98 C. 4.00 4.00 *Addition Temperature to High Intensitymixer **parts per hundred resin

TABLE 2 Design of Experiments for Torque Rheometer Design of ExperimentsBrabender Torque Rheometer: 65 g, 60 rpm Developmental Process AidCommerical Process Aid (nominally Deg C. (nominally 80% MMA/20% BA) 70%MMA/30% BA) 190 X X 190 repeat X 185 X 180 X X 180 repeat X 175 X 170 X170 repeat X 165 X 160 X

TABLE 3 Fusion Time - Torque Rheometer Fusion Time [min] BrabenderTorque Rheometer: 65 g, 60 rpm Developmental Process Aid CommericalProcess Aid (nominally Deg C. (nominally 80% MMA/20% BA) 70% MMA/30% BA)190 0.90 0.70 190 repeat 0.70 185 0.80 180 1.23 0.87 180 repeat 0.93 1751.07 170 1.20 170 repeat 1.17 165 1.30 160 1.43

TABLE 4 Fusion Matches Match #1 - CPA @ 190 C. = DPA @ 180 C. = DPA @180 C. Repeat 0.90 0.87 0.93 Match #2 - CPA @ 180 C. = DPA @ 170 C. =DPA @ 170 C. Repeat 1.23 1.20 1.17

What is claimed is:
 1. A foamed material comprising: a. 50 to 99 percentpolyvinyl chloride (PVC) or chlorinated polyvinyl chloride (CPVC) foammatrix; b. 1 to 15 weight percent of one or more acrylic copolymersprocess aids for forming PVC or CPVC foamed materials, said acryliccopolymer process aid having a configuration selected from the groupconsisting of random, block, tapered, comb, and star copolymers, whereinsaid acrylic copolymer process aid consists of from 50 to 75 weightpercent of methyl methacrylate units, and from 25 to 50 weight percentconsisting of at least one other different monomer selected from thegroup consisting of alkyl acrylate and styrene-monomer, wherein saidacrylic copolymer process aid has a Tg of less than 80° C., a weightaverage molecular weight from 2 million to 10 million g/mol, and issolid; c. 2 to 10 weight percent of filler selected from the groupconsisting of cellulosic fibers, calcium carbonate, rosin, limestone,aluminum trihydrate, quartz, and silica; and d. optionally otheradjuvants selected from the group consisting of dyes, colorants, UVstabilizers, anti-oxidants, pigments, heat stabilizers, PVC homopolymer,acrylic process aids, plasticizers, lubricants, calcium stearate, metalrelease agents, polyethylene, paraffin wax, impact modifiers, and TiO₂;the total adding to 100 weight percent.
 2. The foamed material of claim1, wherein said acrylic copolymer consists of from 50 to 70 weightpercent of methyl methacrylate units, and from 30 to 50 weight percentcomprising at least one other acrylic monomer.
 3. The foamed material ofclaim 1, comprising 3 to 12 weight percent of said acrylic copolymer. 4.The foamed material of claim 1, wherein said acrylic copolymer has a Tgof less than 70° C.
 5. The foamed material of claim 1, wherein saidacrylic copolymer has a Tg of less than 65° C.
 6. The foamed material ofclaim 1, wherein said acrylic copolymer has a weight average molecularweight of from 4.0 million to 7.0 million.
 7. The foamed material ofclaim 1, comprising a sized article.
 8. The foamed material of claim 1,wherein the foam cell size is from 10 to 250 microns.
 9. The foamedmaterial of claim 1, wherein said acrylic copolymer is miscible with PVCand/or CPVC.
 10. A foamed material consisting of: a. 50 to 99 percentpolyvinyl chloride (PVC) or chlorinated polyvinyl chloride (CPVC) foammatrix; b. 1 to 15 weight percent of one or more acrylic copolymersprocess aids for forming foamed PVC or CPVC materials, said acryliccopolymer process aid having a configuration selected from the groupconsisting of random, block, tapered, comb, and star copolymers, whereinsaid acrylic copolymer process aid consists of from 50 to 75 weightpercent of methyl methacrylate units, and from 25 to 50 weight percentconsisting of at least one other different monomer selected from thegroup consisting of alkyl acrylate and styrene, monomer, wherein saidacrylic copolymer process aid has a Tg of less than 80° C., a weightaverage molecular weight from 2 million to 10 million g/mol, and issolid; c. 2 to 10 weight percent of filler selected from the groupconsisting of cellulosic fibers, calcium carbonate, rosin, limestone,aluminum trihydrate, quartz, and silica; and d. optionally otheradjuvants selected from the group consisting of dyes, colorants, UVstabilizers, anti-oxidants, pigments, heat stabilizers, PVC homopolymer,acrylic process aids, plasticizers, lubricants, calcium stearate, metalrelease agents, polyethylene, paraffin wax, impact modifiers, and TiO₂;e. optionally blowing agent(s) or their residues, f. optionallynucleating agent(s) or their residues, the total adding to 100 weightpercent.